Low-Valent Niobium-Mediated Double Activation of C−F/C−H Bonds: Fluorene Synthesis fromo-Arylated α,α,α-Trifluorotoluene Derivatives

Reactivity of a palladium fluoro complex towards silanes and Bu3SnCHCH2: catalytic derivatisation of pentafluoropyridine based on carbon–fluorine bond activation reactions

The chloro and azido complexes trans-[PdCl(4-C5NF4)(PiPr3)2] (3) and trans-[Pd(N3)(4-C5NF4)(PiPr3)2] (4) can be prepared by reaction of [PdF(4-C5NF4)(PiPr3)2] (2) with Et3SiCl or MeSiN3, respectively. In contrast, reactions of 2 with Ph3SiH or Me2FSiSiFMe2 give the products of reductive elimination 2,3,5,6-tetrafluoropyridine (5) or 4-(fluorodimethylsilyl)tetrafluoropyridine (6) as well as [Pd(PiPr3)2] (1). In a catalytic experiment, pentafluoropyridine can be converted with Ph3SiH into 5 in 62% yield, when 10% of 2 is employed as catalyst. Treatment of trans-[PdF(4-C5NF4)(PiPr3)2] (2) with Bu3SnCH=CH2 in THF at 50 degrees C results in the formation of [Pd(PiPr3)2] (1) and 4-vinyltetrafluoropyridine (7). Complex 2 is also active as a catalyst towards a Stille cross-coupling reaction of pentafluoropyridine with Bu3SnCH=CH2 to give 4-vinyltetrafluoropyridine (7) with a TON of 6. The molecular structure of the complex 3 has been determined by X-ray crystallography.